1. Field of the Invention
This invention relates to a printing head for a drop-on-demand ink jet printing apparatus and, more particularly, to a compact printing head utilizing an array of successive monomorphic transducer plates interleaved with matching cavity plates which cooperate to selectively eject ink droplets through an array of associated and closely spaced nozzles.
2. Description of the Prior Art
Printers and recorders of various types have been developed which employ a stream of discontinuous droplets. The ink is ejected through a small opening or nozzle as a result of the action of a transducer. A cavity is formed that is partially enclosed by a diaphragm of piezo-electric material to form a chamber. The piezo-electric material has the ability to change shape upon being charged electrically. A channel leads from the chamber to the opening and another channel leads to the chamber so that ink may be supplied thereto. A small charge is applied to the piezo-electric material to alter its shape and thereby cause a drop of ink to be ejected from the chamber and out through the nozzle.
Although prior systems have worked substantially well, improvements are always being sought. One goal consistently pursued is to have the openings of the ink jet printer as close to one another as possible. Obviously, by having the openings close together, one is able to produce more dots per unit area and obtain more refined printing. The barrier in having openings close together is the fact that each chamber of the ink jet printer requires a minimum amount of space. Various designs have been developed in order to have the openings close together.
One attempt has been to increase the number of lines of nozzles whereby the nozzles are staggered relative to one another to form two or more rows. A disclosure of this nature is found in the U.S. Pat. No. 4,418,356 to Reece. Although this has the advantage of having more nozzles per line, the disadvantage is that synchronization is required between the enabling of the piezo-electric elements and movement of the medium being printed with the result that the price must be paid in electronics.
Another way of attempting to increase the density of nozzles is to have elongated chambers as opposed to circular chambers. Such a construction is disclosed in the patent to Italiano et al, U.S. Pat. No. 4,415,909 which provides an arrangement of nozzles in a symmetrical pattern. The problem with this configuration is that efficiency is lost.
Another scheme attempted is to have not only longitudinally shaped chambers, but to have them in a fanning arrangement as disclosed by one of the embodiments of the patent to Martner, U.S. Pat. No. 4,468,680. The disadvantage with this configuration is not only the inefficiency as a result of having elongated chambers but also the fact that the chambers are further removed from the nozzles.
Yet another construction is disclosed in the patent to Louzil, U.S. Pat. No. 4,455,560, according to which the piezo-electric elements are staggered relative to one another. However, even such staggering does not provide a significant improvement in decreasing the mass of the overall print head.
More recently, a transducer to an ink jet printer has been developed according to which the chamber portion of the ink supply occupies significantly less space. In prior devices, the transducer was composed not only of a piezo-electric material but also included a diaphragm layer between the chamber and the piezo-electric material. The diaphragm was made of a conductive material such as metal and was used to control the movement of the piezo-electric material. However, as disclosed in commonly assigned copending applications, the diaphragm normally associated with the transducer is no longer required. These are, respectively, applications of Hubbard, Ser. No. 700,582, filed Feb. 11, 1985, entitled "Single Element Transducer For An Ink Jet Device" and of Cruz-Uribe et al, Ser. No. 772,109, filed 9-3-85, entitled "Notched Piezo-electric Transducer For An Ink Jet Device". Rather, as disclosed in each of the aforesaid applications, the pressure pulsing is accomplished by using a ceramic piezo-electric element that has either a notched configuration or a dome-shaped configuration. Furthermore, the chamber portion of the ink supply utilized with the one element transducer also occupies less space thereby achieving a two-fold reduction in the space necessarily occupied by the transducer.
Thus, throughout the specification, the terms "monomorph" and "monomorphic" refer to a one-piece transducer used to create the pressure for the ink droplets. Such a one-piece construction is in contrast with "Biomorph" (a trademark of the Clevite Corporation of Cleveland, Ohio) or "biomorphic" transducers which are of two-piece construction utilizing a piezo-electric crystal bonded to a diaphragm of conductive material.